1. Field of the Invention
The present invention relates to an improvement in the performance of a suction and/or discharge mechanism of a refrigerant gas compressor which is provided with a valve plate located between a cylinder block having compression chambers for suction and compression of a refrigerant gas and a cylinder head having therein a suction and a discharge chamber for the refrigerant gas before and after compression, and more particularly, to a particular configuration of suction and/or discharge ports formed in the valve plate of the refrigerant gas compressor and cooperating with flapper-type suction and/or discharge valves so as to bring about a decrease in a suction and/or discharge resistance for the refrigerant gas flowing from the suction chamber to the compression chambers of the cylinder block via the suction ports, and/or from the compression chambers to the discharge chamber via the discharge ports.
2. Description of the Related Art
Many refrigerant gas compressors, such as a swash plate type compressor, a wobble plate type compressor, and a vertical crank-type compressor, are known. In general, the refrigerant gas compressor has a cylinder block having therein more than one compression chamber for compressing a refrigerant gas by the operation of compressing elements, such as reciprocating pistons, a cylinder head having therein a suction chamber for the refrigerant gas before compression and a discharge chamber for the refrigerant gas after compression, and a valve plate arranged between the cylinder block and the cylinder head as a partition therebetween. The valve plate has suction ports for communicating between the suction chamber of the cylinder head and respective compression chambers of the cylinder block, and discharge ports for communicating between respective compression chambers and the discharge chamber of the cylinder head. The suction ports of the valve plate are opened and closed by suction valves attached to the valve plate. Similarly, the discharge ports of the valve plate are opened and closed by discharge valves attached to the valve plate. Each of the suction and discharge valves is formed as a thin flapper type valve in the shape of an elongated plate having a front portion acting as a lid of the valve and moving toward and away from the associated suction or discharge port, and a base portion fixed to the valve plate by a screw bolt. The front portion of each discharge valve tightly closes the associated discharge port during the suction stroke of the related compressing element within the compression chamber, and opens the discharge port when it is moved away from the discharge port by the pressure of the compressed refrigerant gas during the discharge stroke of the related compressing element. The front portion of each suction valve opens the associated suction port, due to the suction pressure of the refrigerant gas during the suction stroke of the related compressing element, and tightly closes the associated suction port under the influence of the pressure of the compressed refrigerant gas during the discharge stroke of the related compressing element.
In the described conventional refrigerant gas compressor, each of the suction and discharge ports consists of a round port bored in the valve plate.
The movement of the above-mentioned front portion of each valve to open the associated port is carried out in such a manner that it is gradually and resiliently raised from the closed position toward a predetermined position whereat the valve adopts a slanted posture, and is stopped by a retainer plate. Therefore, while the round suction and/or discharge ports are opened by the associated flapper type suction and/or discharge valves in the slanted posture, the refrigerant gas which flows through a part of each of the round suction and/or discharge ports is inevitably subjected to a large flow resistance compared with the gas flowing through the other portion of each of the round suction and/or discharge ports. As a result, for example, in the case of the round discharge port of the valve plate of the conventional compressor, the performance of the refrigerant gas compressor is adversely affected by the various defects described below, with reference to FIGS. 7 through 9.
Referring to FIGS. 7 and 8, which are a partial cross-sectional and a plan view of the conventional discharge valve mechanism of a refrigerant gas compressor, respectively, a valve plate 3 is arranged between a compression chamber 1 and a discharge chamber 2 so as to act as a partition therebetween. The valve plate 3 has a discharge port 14 bored therein for communicating between the compression chamber 1 and the discharge chamber 2. A flapper type discharge valve 5 in the shape of an elongated resilient plate and a retainer plate 6 are arranged in the discharge chamber 2 and attached to the valve plate 3 by a screw bolt 7. A front portion 5a of the discharge valve 5 is disposed so as to close the discharge port 14, and can be raised by the pressure of the refrigerant gas discharged from the compression chamber 1 to a predetermined position whereat the valve 5 is stopped by the retainer 6, as shown in FIG. 7. That is, the retainer 6 determines the amount of upward movement of the front portion 5a of the valve 5.
As previously described, the configuration of the discharge port 14 of the valve port 3 is a true circle. During the discharge stroke of the compressor, the compressed refrigerant gas flows from the compression chamber 1 toward the discharge chamber 2 through the discharge port 14. At this stage, from a macro viewpoint, the flow rate of the refrigerant gas passing through the circular discharge port 14 is approximately equivalent with respect to all positions of the port 14. However, as best illustrated in FIG. 7, the discharge valve 5 fixed, at a base portion thereof, to the valve plate 3 by the screw bolt 7 is allowed to bend only in the lengthwise direction about the fixing position under the pressure of the discharged gas so that the front portion 5a of the discharge valve 5 takes a slanted posture. Accordingly, when viewed in the lengthwise direction of the valve 5, the amount of upward movement of the front portion 5a of the discharge valve 5 from a top face 14' of the discharge port 14 cannot be equal in the diametrical direction of the port 14. As a result, the compressed refrigerant gas leaving the round or circular discharge port 14 and colliding with the slanted front portion 5a of the discharge valve 5 is subjected to an unequal resistance. Thus, the pressure of the refrigerant gas measured at diametrically various positions above the face 14' of the discharge port 14 becomes unequal, as illustrated in FIG. 9.
It will be also understood from FIG. 9 that a large flow resistance to which the discharged refrigerant gas is subjected appears and is distributed in the various position of the port 14 far from the frontmost end of the front portion 5a of the discharge valve 5. Therefore, the following defects are encountered by the conventional refrigerant gas compressor.
(1) During the discharge stroke of the compressor, a part of the compressed refrigerant gas is not discharged, and remains within the compression chamber 1. The remaining gas is then expanded during the subsequent suction stroke of the compressor and thus prevents a sufficient amount of the refrigerant gas from being pumped into the compression chamber 1 from a suction chamber (not shown in FIG. 1). Thus, the suction performance of the compressor is degraded.
(2) During the compression stroke of the compressor, a part of the refrigerant gas which was not discharged from the compression chamber 1 during the preceding discharge stroke, is re-compressed. Thus, excessive compression occurs in the compression chamber 1. Such excessive compression generates a reaction force acting on the compression drive mechanism, such as a piston mechanism. Therefore, the compression drive mechanism always requires more power to compress the refrigerant gas, and thus a loss of power occurs in the operation of the conventional compressor.
(3) Unstable opening and closing motions of the discharge valve 5 occur and, therefore, a pulsation appears in the flow of the discharged refrigerant gas. This pulsation in the flow of the discharged refrigerant gas generates noise.
Similarly, in the case of the suction valve mechanism having round suction ports of the valve plate, a like degradation in the suction performance and a suction pulsation problem are encountered.